Is it possible to change type?
I honestly think "'personality" is a misleading term in MBTI, which is solely based on the concept of cognitive functions. Cognitive functions are mainly brain processes, how your brain interprets information and makes use of it. They are innately born in you since birth. Personality, I believe, is more of the flavor and spice that adds on it.
If you were to try to be another type, you're using your own functions to pretend to be that type. Lol.
But what if you are depressed or suffered a great disaster in your life?
This is where the shadow functions come up. Now, everyone has all 8 functions, but depending on type they use one more than the other or just differently. The main 4 functions can also act unhealthily, like if I use my Te in relation to people too strictly. The other 4 functions you aren't aware of can come up unexpectedly without conscious thought, but it's clear that the function wasn't utilized frequently. You don't really have control over the shadow functions, after all.
Although if it was very damaging, it doesn't seem too difficult to transition from an extrovert to an introvert (and vice versa), but that's still changing the order of your dominant and auxiliary functions. The auxiliary function is a means of support to the dominant function. Functions can act very differently depending on its position of order in the functions.
I can't be an NT! Or even an introvert, I'm not smart!
Every type has their own advantages and disadvantages. But always remember type does not determine intelligence. Not to mention, there are a million kinds of intelligence, and we haven't even properly defined "intelligence" yet. Cognitive functions are just brain processes, specific ones aren't orientated to only a certain intelligence of people. Every function is good in its unique way to gain knowledge and play an important role in the world.
There's a person who's a completely different type from me, we'll never get along!
MBTI is so horribly unreliable in relationships. Since when did type theory dictate which types you can only form relations with? Any type can form relationships with each other, "perfect matches" don't exist.
Of course, cognitive functions can conflict with each other. Learn how they act through their function usage, and form the best possible response to it.
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Just realized I rambled off in the last two answers, oh well. But substantially, I think the intelligence question is the reason for most people not believing the type they are.